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  1. Galaxies and Cosmology
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  3. Galaxies and the Universe - Introduction
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The Polish astronomer, Nicolaus Copernicus — , did not believe in the geocentric model of the Universe either. Copernicus came up with a new theory called the heliocentric system. The discovery of Copernicus led to a complete revision of the knowledge about the world, which had been constructed on the belief that Earth was the centre of the Universe. Now it had to be accepted that Earth was nothing but a planet among the others. In the Heliocentric System the Sun is in the centre and the planets move in orbits around the Sun.

This was something extremely difficult to accept at the time, because it seemed to be opposite to the plausible view that Earth must be the centre of everything. At first, he had just a few loyal believers. Giordano Bruno — was an Italian philosopher and poet. He was convicted of heresy and free-thinking by the Inquisition, imprisoned for 8 years and eventually burnt at the stake for his beliefs. Eventually, one after the other, scientists began to adopt this new system. Since then, his theory has of course been proven correct. Galileo and Kepler were two of the first scientists to find evidence to support the heliocentric system.

Kepler discovered the mathematical description of the movement of the planets around the Sun. The so-called Kepler laws were found by detailed inspection of astronomical observations of the planets performed and written down by Tycho Brahe. These laws accurately describe those in mathematical language. They can be formulated as follows:.

The orbits of the planets are ellipses with the Sun at one focus of the ellipse.

Galaxies and Cosmology

The line joining the planet to the Sun sweeps out equal areas in equal times as the planet travels around the ellipse. The square of the orbital period of a planet around the Sun is proportional to the cube of the semi-major axis of its elliptical orbit. Also shown are the major and minor axis and the foci of the ellipse, and the point place in the orbit closest to the Sun Perihelion and farthest from the Sun Aphelion.

Extra-solar planets are planets that orbit other stars. Astronomers are getting more and more adept at finding them and, as of January , around have been confirmed. It proves that it is quite common for stars to be accompanied by planets.

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We have already stumbled accross several ones that might have similar properties to Earth. If we found a planet with a similar size, temperature conditions and atmosphere as Earth, then it could be possible that the planet harbours extraterrestrial life. To combat this, astronomers have devised clever ways to see planets indirectly, using the parent star. You can also find planets by their gravitational effects. The gravitational effect of the star forces the planets into an orbit around it, but gravity works both ways and the gravitational effect of the planet will be pulling on the star too.

However, using more and more sophisticated ways astronomers already found several dozen of such planets that are Earth-like and are located in the habitable zone of their stars. Not all planets have moons. Mercury and Venus, for example, travel alone around the Sun. However, some planets have plenty. Jupiter has over 60 moons. Our planet has just one moon and it is the only place outside Earth that mankind has visited. Astronomers believe that an object roughly the size of Mars collided with Earth and the Moon was formed from the debris.

Neil Armstrong became the first man on the Moon on July 21st, , which is an impressive feat considering that the Moon is ,km away on average. The Moon is being bombarded with a steady rain of meteoroids, asteroids and comets, as are most planets. While on Earth, falling space objects are usually burnt up in the atmosphere, the Moon is covered in craters because it has no atmosphere.

The battered Moon has a great effect on the Earth. Not only does it control the tides, it also stabilises Earth and reduces the amount that it wobbles on its axis. Galileo Galilei — was an Italian physicist, mathematician, astronomer and philosopher, considered an extremely important figure in the Scientific Revolution. Some of his many achievements include constructing the first telescope. He was in fact observing Jupiter and had discovered its 4 largest moons.

In the Inquisition convicted him of heresy. They forced him to publicly withdraw his support for Copernicus and the heliocentric system and sentenced him to life imprisonment. Due to his advanced age and bad health, that sentence was amended the next day to allow him to serve his sentence under house arrest instead.

Galaxies and the Universe - Introduction

Europa is the smallest but the most interesting moon of Jupiter because it is considered a candidate for harbouring extraterrestrial life. It has about a quarter the size of the Earth. It is covered by an ice crust, below which the largest ocean of the whole Solar System is found.

Universe Size Comparison 3D

It is estimated that this ocean could have a depth of up to 20 km on Earth the deepest point in all oceans is only about 11 km. The necessary energy for these volcanoes is provided either by natural radioactive decay as on Earth in the rocky interior of Europa or by tidal effects caused by nearby Jupiter. Do tiny algae or giant squids!

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We do not know yet. The answer depends on the unknown mechanisms for the origin of life itself as well as on the conditions of Europa. For instance, a spacecraft landing on the icy surface of Europa could search for organic molecules produced by life in the ocean. The ice on Europa is too thick for drilling but geologic processes may transport oceanic components to the surface where it could be found by a space probe.

Not only does Europa have what seems to be liquid water, it also has a thin oxygen atmosphere.

John Gribbin

Yet despite the water and oxygen, living on Europa would still be extremely difficult. The surface receives around mSv of radiation emitted from Jupiter, a fatal dose for humans. One would have to live below the surface, where it is warmer.

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So, here are some definitions: Meteoroids are small rocks in our solar systems with dimensions of less than 10m across. This forms a burning line in the sky. One can find meteorites all over the planet but especially in Antarctica as the meteorites are easy to see on the ice and the cold protects them from geological transformation. Asteroids are bigger. They can have sizes up to many kilometres.

Most of them can be found in the main asteroid belt which orbits the Sun between Mars and Jupiter. Comets are between 1km and 20km long and are mainly made up of ice and dust. This is why sometimes they can be called 'dirty snowballs'. They have extremely elliptical orbits and, because of this, they spend most of their time far out in the Solar system, beyond Pluto. You can often see two tails on a comet. It quite likely originated from Mars.

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The cube shown has 1cm sides. They contain stars, gas, black holes, and dark matter — a component of the universe which has not yet been identified. A good understanding of galaxies is critical for a good understanding of the Universe and its contents. By studying galaxies and cosmology, we ultimately seek to understand how a very smooth universe at early times produced the wealth of structure we see now.

This lecture series gives an introduction into galaxies and cosmology. In this, we will ask and try to answer! We will cover topics including but not limited to those related to mapping our Milky Way, the dynamics and structure of stellar systems, galaxy groups and clusters, the presence of dark matter, central supermassive black holes, the expanding Universe, the formation of structure, and the earliest galaxies.

See Schedules bachelor Astronomy Blackboard will be used to post the lecture slides, homework assignments, and any extra materials. Students should enroll on Blackboard before the first lecture. There are probably more than billion 1. Most are 1, to , parsecs in diameter and usually separated by distances on the order of millions of parsecs or megaparsecs. Intergalactic space the space between galaxies is filled with a tenuous gas of an average density less than one atom per cubic meter. The majority of galaxies are organized into a hierarchy of associations known as groups and clusters, which, in turn usually form larger superclusters. At the largest scale, these associations are generally arranged into sheets and filaments, which are surrounded by immense voids.

On December 12, , astronomers, working with the Hubble Space Telescope, reported that the most distant known galaxy, UDFj, is now estimated to be even further away than previously believed. You must be logged in to post a comment.